PSI - Issue 29

Mauro Sassu et al. / Procedia Structural Integrity 29 (2020) 8–15 Mauro Sassu / Structural Integrity Procedia 00 (2019) 000 – 000

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to partia l or tota l collapses is the ra in penetration, joined with freeze-thaw(Croce et a l 2019). Traumatic events like earthquakes or floods can producefailures (Puppio et a l 2020), but a lso anthropic causes, like works in the nearby of the wa lls (Solarino et a l 2018) are able to generate collapses. In archaeological context thoseaspects are exacerbated by the vulnerability of the entire constructive system. Indeed the role of the structural engineer is not only to prevent the collapses, but also to conserve carefully the constructive memory “imprisoned” in the wa lls or the structural features, including construction details a lso in low technology elements(Sassuet al 2016): their level of accuracy, howmaterials or elements were chosen, positioned and refinished. The possibility of testify the current state of the historical constructions and infrastructures is recently increased, thanks to the strongevolutionof ICT disciplines: digital photos, movies, 3Dsurveys with info characterizedby high level of definition (Mistretta et a l 2019), affordable GIS sa tellite procedures (Amirebrahimi et a l 2016, Pucci et al 2019) and BIM approaches (Fiamma et al 2019) can furnish a virtual re-constructions of the investiga ted elements. Although the problem of their reliability over time is a crucial issue: how many digital documents, photos, movies drawn up a few decades ago, are today available? An how it can be conserve in a rea listic efficient way a ll those documentations, ensuring procedures that will permit , after further decades or centuries, the integrity of the info on restora tion works, in order to avoidconfusion ormisunderstanding to the future scientists? Referring to the structural integrity of archaeologicalwa lls, one of the more dangerous phenomenon is the out-of plane rocking. From classic Ho usner’s approach (Housner, 1964), many contributions have beendeveloped (Giresini et a l 2018, Giresini 2019), It canobserve that dry stone walls arefrequent in the archaeological contexts, so appropriate models (Casapulla et a l 2018) should be used to prevent local failures. Both aspects, to conserve as a “stonearchive” the constructivefeatures of a masonry structure in an archaeological element and to ensure a proper safety and integrity level of thee wa lls a long the centuries, are crucial issue for the designer of the restorationprocedure. In the past well-known and appreciated discovering were accompanied by nor reversible reconstructions, we can consider the famous example of Knossos Pa lace in Creta Island discovered in early ‘900 by A. Evans, in which the reconstructions were supported by extensivereinforcedconcrete elements (recognizable but not much respectful and not reversible). Or we can evaluate in this sense the reinforcements of the Colosseum in Rome in ‘800 , as the spur of Speer: a full clayunit buttress (recognizable but not completely respectful andnot reversible); we cancompare it with the buttress of arches done by Va ladier (recognizable, an interesting respectful interpretation of the use of clay units but anywaynot reversible). Three examples of the so called “Three R strategy”consolidation techniques are here explained (Sassuet al 2017): they canbe defined as respectful, recognizable and reversible operatingmodes. a) RESPECTFUL consolidation means: if it does not invade the origina l hea lthy parts of the building, the reconstructedparts are not dissonant to the original ones and the reconstructedparts do notweaken the original ones. b) RECOGNIZABLE consolidation means: if the reconstructed part differs from the origina l one, a lbeit with technical precautions that "do not visually disturb" the construction. c) REVERSIBLEconsolidationmeans: whether the rebuilt part canberemoved in the futurewithout damaging the origina l hea lthyones A RESPECTFUL, RECOGNIZABLEANDREVERSIBLECONSOLIDATIONoccurs when The visitor hardly distinguishes the origina l parts from the reconstructed ones or, if he distinguishes them, the reconstructions are visua lly RESPECTFUL. The scholar succeeds in distinguishing the origina l parts from those reconstructed through a series of clearly RECOGNIZABLE technical devices. The owner of the building can make the interventionREVERSIBLE: in the futuredisassemble it to put in placeanother better one discovered. 2. A set of case studies inUNESCOsites The first two examples are located in SouthernArabic Peninsula (Dhofar district – Sultanate ofOman): thecity of Sumhuram in the UNESCOKhor Rori area built between IVB.C. andVIA.D. and thecityofAlBalid in theUNESCO Zafar area, built between IXand XIII A.D. (cited a lso by Marco Polo in il Milione with the name of Zafar. The first one was a small emporium city over a hill surrounding the lagoon of Khor Rori, the second was a large city with relevantmilitarycity wa lls a long the Indian Ocean